1. Field of the Invention
The present invention relates to an induction coil structure for a wireless charger, and more particularly, to an induction coil structure with excellent inductance and resistance characteristics for a wireless charger, to improve the performance of the wireless charger.
2. Description of the Prior Art
In an induction type power supply system, a supplying-end device of the power supply system transmits power by oscillating and generating sinusoidal wave on a resonance circuit and the sinusoidal wave transmits power to a receiving-end device of the power supply system. The resonance circuit is composed of a resonance capacitor and a supplying-end coil with inductance characteristics, which are driven by a switch circuit. The receiving-end device also includes a resonance circuit composed of a receiving-end coil and a resonance capacitor, for receiving the power transmitted from the supplying-end device to achieve wireless power transmission.
In general, the resonance circuit is composed of coils and the capacitor connected in series. At the supplying-end device, when power switch signals are inputted to both ends of the resonance circuit (i.e., the full-bridge driving mode) or only one end of the resonance circuit (i.e., the half-bridge driving mode), oscillation may be generated on the resonance circuit. Ideally, both the inductance and the capacitance of the resonance circuit reach infinitely large values so that the DC component and AC component of the power switch signals inputted to the resonance circuit may not result in short circuit between the two ends of the resonance circuit, and the power may thereby be efficiently transmitted to the receiving-end device. Though the capacitors obtained in the market may have enough capacitance values, the inductance value of the coils may vary in magnitude due to the differences in the width, length or winding way of the coils. When the inductance value is too small, the AC component of the power switch signals may pass through the coils directly to result in short circuit. A large instantaneous current may thereby be generated between the resonance circuit and the driving circuit, and the circuits may easily be burnt due to the short circuit phenomenon. In addition, the instantaneous current may produce large ripples on the voltage of the coil signal, which may cause electromagnetic interference (EMI) problems. Furthermore, since currents may pass through the resonance circuit when the resonance circuit operates and the coils of the resonance circuit usually have internal impedance, power loss may be generated when the currents pass through the internal impedance of the coils.
Therefore, current coil designs aim at a higher inductance value and lower resistance value in the coils. The conventional ways of increasing inductance are increasing the winding number of the coils and combining the coils together with the magnetic conductor. The conventional ways of reducing the resistance are using thicker coils and reducing the length of the coils as possible. With the same winding area, the usage of thicker coils limits the winding length of the coils. In such a situation, making a choice between the inductance and the resistance values to obtain a preferable length of coils and designing the winding way of coils to let the coils to effectively work with the magnetic conductor have been the major issues in this art that need to be dealt with.